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Computing Machinery I Assignment 2 Solution




Bit Reversal using Shift and Bitwise Logical Operations




Create an ARMv8 assembly language program that implements the following program:




#include <stdio.h




int main()

{

register unsigned int x, y, t1, t2, t3, t4;




Initialize variable x = 0x07FC07FC;



Reverse bits in the variable
Step 1
t1 = (x & 0x55555555) << 1;

t2 = (x 1) & 0x55555555;

y = t1 | t2;




// Step
2


t1
= (y
&
0x33333333) << 2;
t2
= (y
2) & 0x33333333;
y = t1 | t2;
// Step
3


t1
= (y
& 0x0F0F0F0F) << 4;
t2
= (y
4) & 0x0F0F0F0F;
y = t1 | t2;
// Step
4


t1
= y << 24;
t2
= (y
& 0xFF00) << 8;
t3
= (y
8) & 0xFF00;
t4
= y 24;



y = t1 | t2 | t3 | t4;




// Print out the original and reversed variables printf("original: 0x%08X reversed: 0x%08X\n", x, y);




Return 0 back to OS return 0;
}




Be sure to use 32-bit registers for variables declared using int. Use m4 macros to name the registers to make your code more readable. Name the program assign2a.asm. Optimize your code so that it uses as few instructions as possible.




Also run the program in gdb, displaying the contents of key registers as the program executes; you should show that the algorithm is working as expected. Also print out the original and reversed values both in hexadecimal and in binary, just before the program exits. Capture the gdb

session using the Unix command script and name the output file script.txt.




Create a second version of the program (called assign2b.asm) that uses 0x7F807F80 for the x variable. Also create a third version of the program (called assign2c.asm) that uses 0x01FF01FF x variable.




Other Requirements




Make sure your code is properly formatted into columns, is readable and fully documented, and includes identifying information at the top of each file. You must comment each line of assembly code. Your code should also be well designed: make sure it is well organized, clear, and concise.




New Skills Needed for this Assignment:




Use of bitwise logical and shift operations




Understanding of hexadecimal and binary numbers




Submit the following:




Your assembly source code files for the 3 programs, and your script output file. Use the Assignment 2 Dropbox Folder in D2L to submit electronically. The TA will assemble and run your programs to test them. Be sure to name your programs and script file as described above.
Computing Machinery I




Assignment 2 Grading







Student:__________________________________________













Functionality:






Bit reversal step 1
3
______


Bit reversal step 2
3
______


Bit reversal step 3
3
______


Bit reversal step 4
5
______


Display to screen
3
______


Optimization
2
______


Script showing gdb session
3
______


Complete documentation and commenting
4
______


Formatting (use of columns and white space)
4
______


Design quality
2
______


Version 2
2
______


Version 3
2
______


Total
36
______
_____%

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